There is a case that a self-dispersing pigment is used in a water-based ink for ink jet recording. Since the self-dispersing pigment does not need to use in combination with a polymer pigment dispersant, it can prevent an increase in viscosity of the water-based ink and the water-based ink is superior in ejection stability and storing stability. The self-dispersing pigment can be obtained by treating a pigment to bind with at least one type of hydrophilic group such as a phosphate group, a carboxylic group, or a sulfonate group or a salt thereof. A self-dispersing pigment obtained by treating a pigment specifically by a phosphate group among these hydrophilic groups (hereinafter, also referred to as “phosphate group-modified self-dispersing pigment”) can obtain a high optical density (OD) as compared with a self-dispersing pigment obtained by treating a pigment by a carboxylic group or a sulfonate group.
On the other hand, the water-based ink using the self-dispersing pigment obtained by treating a pigment by a phosphate group has a problem in that its redispersibility is not favorable. “Redispersibility” is solubility and dispersibility of a solid substance generated by evaporation of a water-based ink to dryness in the case where the solid substance re-contacts with a water-based ink. When the water-based ink is unfavorable in redispersibility, there is a problem in ejection stability in the case where the water-based ink is evaporated to dryness in an ink flowing path or in proximity to the nozzle of an ink-jet head. There is a demand for the water-based ink for ink jet recording using the phosphate group-modified self-dispersing pigment to further improve an optical density (OD).